1. Field of the Invention
The present invention relates to a retainer for a tapered roller bearing, a method of manufacturing a retainer, and a tapered roller bearing.
2. Description of the Related Art
Driving force of an automobile engine is transmitted to wheels through an intermediation of a power transmission system including any one or all of a transmission, a propeller shaft, a differential, and a drive shaft.
In the power transmission system, there is used in many cases, as a bearing for supporting a shaft, a tapered roller bearing excellent in load capacity with respect to radial load, and in impact resistance. As illustrated in FIG. 12, the tapered roller bearing generally includes an inner race 2 having a tapered raceway surface 1 on an outer peripheral side thereof, an outer race 4 having a tapered raceway surface 3 on an inner peripheral side thereof, a plurality of tapered rollers 5 arranged so as to be rollable between the inner race 2 and the outer race 4, and a retainer 6 for retaining the tapered rollers 5 at predetermined circumferential intervals.
The retainer 6 includes a radially-larger-side ring portion 6a, a radially-smaller-side ring portion 6b, and brace portions 6c for coupling the ring portions 6a and 6b to each other. The tapered rollers 5 are accommodated in pockets 6d formed between the brace portions 6c adjacent to each other in a circumferential direction.
In the tapered roller bearing, the tapered rollers 5 and the respective raceway surfaces 1 and 3 of the inner race 2 and the outer race 4 are held in linear contact with each other, and the tapered roller bearing is designed such that the respective raceway surfaces 1 and 3 of the inner and outer races and a roller center O accord with one point (not shown) on an axial center P.
Thus, the tapered rollers 5 are pressed to a larger end side when load acts thereon. In order to bear the load, a flange portion 7 protruding to a radially outer side is provided on a radially larger side of the inner race 2. Further, in order to prevent the tapered rollers 5 from falling to a smaller end side until completion of the incorporation of the bearing into a machine or the like, there is provided a flange portion 8 protruding also to the smaller end side of the inner race 2.
Under the above-mentioned circumstances, there has been proposed to achieve longer life of the bearing by increasing the number of the rollers or by increasing the length of the rollers so as to increase load capacity within the same dimension as compared to the currently-used bearing. However, in the currently-used structure, as described above, in terms of assembly of the bearing, the flange portion (small flange) 8 is provided on the radially smaller side of the raceway surface of the inner race. Therefore, the flange portion 8 imposes restriction on an increase in the length dimension of the tapered rollers 5. Further, the tapered rollers 5 are retained by the retainer 6 as described above, and the brace portions 6c of the retainer 6 are interposed between the tapered rollers 5 adjacent to each other in the circumferential direction. Thus, the brace portions 6c impose restriction also on the rollers to be increased in number. As described above, there has been conventionally a limitation on an increase in the load capacity.
In view of the above, in some conventional tapered roller bearings, a flange portion (small flange) on a radially smaller side is omitted in an inner race (Japanese Utility Model Application Publication No. 58-165324). When the flange portion on the radially smaller side is omitted in the inner race, it is possible to secure a larger axial length of the tapered rollers correspondingly to a size of the flange portion thus omitted, and hence possible to achieve an increase in the load capacity.
Further, as a conventional technology for increasing load capacity of a tapered roller bearing, there is known a method of narrowing each gap between rollers to set the number of rollers equal to the number of rollers of a full complement roller bearing (Japanese Patent Application Publication No. 2005-351472).
However, when the flange portion (small flange) on the radially smaller side is omitted, the tapered rollers 5 fall to the smaller end side before completion of the incorporation into a machine or the like. That is, an assembly including the inner race, the rollers, and the retainer cannot be formed. As a countermeasure, in Japanese Patent Application Publication No. 2008-121744, on the radially larger side of the retainer, there are provided hook portions to be engaged with the radially larger side of the inner race.
That is, an assembly including the inner race, the rollers, and the retainer is formed through providing such structure that the hook portions are provided on the radially larger side of the retainer, and a circumferential groove into which the hook portions are hooked is formed in a radially outer surface of the inner race on a radially larger side thereof. Further, the bearing having the above-mentioned structure is not different from a conventional tapered roller bearing (tapered roller bearing including no hook portions) in handling the bearing. Still further, through setting a full complement roller bearing condition in the bearing provided with the above-mentioned hook portions, it is possible to increase the number of rollers, and to increase the load capacity.
Description is made of a method of manufacturing a retainer including no hook portions. In this case, the retainer is formed using two dies combined with each other in an axial direction. As illustrated in FIGS. 13A and 13B, the retainer is formed using a mold device which includes a first die (upper die) 11 arranged on the radially outer side and a second die (lower die) 12 arranged on the radially inner side. That is, as illustrated in FIG. 13A, the first die 11 is placed on top of the second die 12, and a resin is filled into a cavity 13 formed by the first die 11 and the second die 12, and then is pressurized. In this manner, the retainer is formed.
After the retainer is formed, separation work is performed on the mold device. In this case, first, as illustrated in FIG. 13B, the first die 11 is moved away from the second die 12 while being slid toward an axial center in an arrow “A” direction. In this manner, the first die 11 is separated from the retainer 6, and the retainer 6 adheres to the second die 12. After that, the retainer 6 is pushed out to the radially smaller side from the radially larger side, and accordingly the retainer 6 is removed from the second die 12.
However, as illustrated in FIG. 9, in a case where hook portions 15 are provided in the retainer 6, the retainer 6 as a formed product cannot be removed from the mold device illustrated in FIGS. 13A and 13B because the hook portions 15 impede (interfere with) the mold device.
In this context, a mold device illustrated in FIGS. 10A, 10B, and 10C is set so as to enable even the retainer 6 including the hook portions 15 to be removed from the mold device. FIG. 10A is a sectional view taken along a region for forming the brace portion 6c. FIG. 10B is a sectional view taken along a region for forming the pocket 6d. FIG. 10C is a sectional view taken along a region for forming one of the hook portions 15.
That is, as illustrated in FIG. 11, when “B” represents an outer diameter of the radially-smaller-side ring portion 6b of the retainer (maximum outer diameter of the radially-smaller-side ring portion 6b of the retainer) and “C” represents an inner diameter of each of the hook portions 15, a relationship of B<C is satisfied, and the mold device is formed into a hollow shape so as to eliminate axial interference when a formed product (retainer 6) is removed from the lower die 12. With this, the retainer 6 can be removed.
However, the mold device illustrated in FIGS. 10A, 10B, and 10C is limited to use only for the retainer 6 satisfying the relationship of B<C. Accordingly, limitations are imposed on a design for dimensions of the hook portions 15, and hence it is difficult to adapt the retainer for various designs. That is, in a design in which the retainer has a small angle, and in a design in which the pockets each have a small dimension in the axial direction of the retainer, it is inevitably difficult to establish the relationship of B<C, which may hinder formation of the structure in which the inner diameter of the hook portion and a region to be hooked (hook groove portion) formed on the radially larger side of the inner race are hooked to each other.
It is possible to provide a tapered roller bearing optimum as a bearing for supporting a shaft of a power transmission system of an automobile, and to provide a retainer available for such a bearing. Further, in a method of manufacturing a retainer, stable assembly is possible, and hence the assembly property can be increased.